Loud-speaker enclosures



Sept. 15, 1959 .1. NIGRO LOUD-SPEAKER ENCLOSURES 2 Sheets-8119s; 1

Filed Sept. 27, 1956 [HI] I INVENTOR. dbH/v Mame Arron/Fri.

Sept. 15, 1959 J. NIGRO LOUD-SPEAKER ENCLOSURES 2 Sheets-Sheet 2 FiledSept. 27, 1956 INVENTOR.

JoH/v MG/PO. BY WW6 01414 (7W 2' ATTORNEY-5'.

United States Patent LOUD-SPEAKER ENCLOSURES John Nigro, Florham Park,NJ. Application September 27, 1956, Serial No. 612,409 12 Claims. (Cl.181- 31) This invention relates to sound reproducing devices andparticularly to loudspeaker apparatus comprising a housing and anelectrically operable loudspeaker for translating electrical signalsinto sound vibrations with high fidelity.

It is well known that different electrically operable loudspeakersproduce audible sounds with diiferent amounts of distortion dependingupon the frequency of the sounds. Thus, speakers with small diaphragmsor cones translate high frequency, e.g. 5000-l5,000 c.p.s., signals withless distortion than speakers with large diaphragms whereas suchspeakers with large diaphragms translate low frequency, e.g. -500c.p.s., with less distortion than such speakers with small diaphragms.Some types of speakers operate over a relatively large range offrequencies, e.g. 6012,000 c.p.s., with low distortion, but suchspeakers do not provide distortionless operation at the extreme ends ofthe audible frequency range. Accordingly, for high fidelity operation,it is customary to employ two or more speakers, separately or coaxially,connected to the electrical signal amplifier by electrical cross-overnetworks which separate the signals by frequency and supply them to thespeaker providing substantially distortionless operation for aparticular signal. For example, one speaker, having -a large diaphragm,may be operated only by signals having frequencies in the range from30100() c.p.s. whereas the other speaker, having a smaller diaphragm maybe operated only by signals having frequencies in the range from1000-15,000

c.p.s.

Furthermore, each speaker normally is resonant at some frequencyin the.audible range so that, unlessprecautions are taken, signals at and nearthe resonant frequency willbe translated in incorrect volume ratio withrespect to signals of other frequencies.

The translation efficiency of a speaker without a housing or battle is10w; In addition, a housing or baflie is desirable not only to modifythe operation of the speaker at its resonant frequency but also tosuppress the back waves produced by the speaker and which causedistortion depending upon the mounting and location of the speaker.

When a speaker is mounted in a housing or on a bafile its ability toproduce audible sounds without distortion is alfected by the area andconfiguration of the face of the bafile or the housing, the presence ofa'chamber in the housing which resonates in the audible frequency range,the amount of movement of the, speaker diaphragm, the air pressure onopposite sides of the diaphragm, the path'length and volume from therear'to the front of the diaphragm and other factors. For these reasons,although known types of housings and bafiles improve the performance ofspeakers in certain respects, they create other problems and providedistorted performance under conditions normally encountered. Forexample, so-called' infinite baflle systems, which as a practical matterare v finite in size, vary in response with frequency and power due tothe size of the panel on "ice which the speaker is mounted and the useof a closed chamber which is resonant at certain frequencies and whichprovides different air pressures on the opposite sides of the speakerdiaphragm when in motion and hence a symmetrical movement of thediaphragm. Other systems employing chambers, ports, etc. cause similardifficulties. Horn type enclosures are capable of distortionlessradiation only over an octave dependent upon the frequency range forwhich they are designed, and as the power requirements increase, thefrequency range for distortionless radiation becomes smaller.

In the loudspeaker apparatus of my invention, the loudspeaker is mountedin a housing comprising a pair of chambers, one of the chambers beinginterconnected with the other by one-way valve means which permits airto pass from said one chamber to the other and a portion of a wall ofsaid one chamber being formed by the diaphragm or cone of the speaker,said chambers being otherwise substantially airtight. Such anarrangement provides symmetrical loading and hence, undistorted movementof the diaphragm. In addition, the valve means prevents the occurrenceof undesirable resonance in the chambers.

In the preferred embodiment of the invention, the face of the wall onwhich the speaker is mounted is as small as possible so as to avoid thedifiiculties wln'ch are encountered with bafiies of larger area. Thus,the width of the wall or panel is made substantially or approximatelyequal to the width of the diaphragm.

Furthermore, in order to provide the desired coupling of the speaker tothe air, the speaker is arranged so as to face the corner formed by twomutually perpendicular surfaces or a flat surface adjoining a pair ofsurfaces perpendicular thereto and the angle of the face of the speakerwall and the location of the speaker is such that an air column of thedesired figuration is provided in front of the speaker. Preferably, thetwo mutually perpendicular surfaces are a corner of a room, and the fiatsurface is a wall of a room and the other pair of surfaces perpendicularthereto are formed by extensions on, the housing. When the speaker facesa corner of the room, improved sound dispersion is obtained.

It is one object of the invention to provide a loudspeaker housing whichwill provide symmetrical loading on the loudspeaker diaphragm or coneand yet will suppress back waves produced thereby.

It is a further object of the invention to provide a loudspeaker housingwhich has no undesirable resonant structures.

It is a further object of the invention to provide a loudspeaker housingwhich, when properly positioned with respect to adjacent surfaces, willprovide good speaker coupling and sound dispersion.

These and other objects of the invention will be apparent from thefollowing detailed description of the preferred embodiments of theinvention, which description should be considered in connection with theaccompanying drawings in which: 7

Figs. 1-3 are respectively rear elevation, vertical section andhorizontal section views of the preferred embodiment of the invention;

Fig. 4 is an enlarged cross-sectional view of one form of valve meanswhich may be employed in the various embodiments of the invention;

Fig. 5 is a horizontal sectional view of a further embodiment of theinvention; and

Figs. 6 and 7 are respectively rear elevation and vertical section viewsof a further embodiment of the invention.

Figs. 1-3 illustrate the preferred embodiment of the invention and arerespectively elevation, vertical section, and horizontal section views.The embodiment shown in these figures is particularly adapted for use ina corner of a room and provides both good sound dispersion throughoutthe room and good acoustical coupling. Futhermore, the housing may besimpler because it is unnecessary to provide any extensions thereon forforming an air column in front of and below the loudspeaker.

As shown in Figs. 1-3, the loudspeaker 10, which has a conicaldiaphragm, is maintained so that it faces into the corner formed betweentwo mutually perpendicular surfaces 11 and 12 of the walls of the room.The fioor 13 of the room forms a further surface which is perpendicularto the surfaces 11 and 12. Of course, the surfaces 11-13 may be formedby bafiles or extensions on the housing 14, but in order to reduce thesize of complexity of the housing 14, the walls and floor of the roomare utilized to provide the desired operation.

The housing 14 comprises a first wall 15 having an aperture thereinwhich is closed by the diaphragm of the speaker 10. The front surface ofthe Wall 15 faces into the corner formed by the surface 11 and 12, andit tilts away from the corner from the base end 16 to the upper end 17,the surface of the wall 15 intersecting the floor 13 and hence the basewall 18 at an angle preferably in the range from 7080. In the embodimentshown in Figs. 1-3, the angle is designated by the letter a and isapproximately 75 By disposing the surface of the wall 15 in this manner,an air column or cavity having the desired figuration is formed inbetween the center 19 of the loudspeaker and the floor 13, the aircolumn not being surrounded on all sides but being bounded by thesurfaces 11 and 12, the floor 13 and the front surface of wall 15. Ingeneral, the volume of this air column should be approximately equal totwice the volume of a cone having the shape and size of the diaphragm ofthe speaker 10 and approximately equal to the volume of the chambercontaining the diaphragm 10. Such relationship aids in providing thedesired air pressure on the opposite sides of the diaphragm on theloudspeaker 10 and in providing the desired coupling of the speaker 10to the air. The air column acts as a loading column for the speaker andthe loading may be varied by adjusting the distance of the wall from thecorner formed by the surfaces 11 and 12.

The housing 14 also comprises joining walls 2025 which with the baseWall 18 and first wall 15 form a first chamber 26 containing thediaphragm of the loudspeaker 10. As mentioned above, the volume of thischamber 26 should be approximately equal to the volume of a cone havingthe shape and size of the conical diaphragm of the loudspeaker 10.

The housing 14 also comprises a top wall 27 which with the first wall15, the side walls 20 and 24, the front wall 22 and the intermediatewall form a second chamber 28. Walls 20, 21 and 22 form a third chamberor cavity 29 and walls 22, 23 and 24 form a fourth chamber or cavity 30.Both of the chambers 29 and are open at their upper ends, theintermediate wall 25 being cut away for this purpose so that air maypass freely from chambers 29 and 30 into and out of the chamber 28. Forthis reason, the chambers 29 and may be considered as separate chambersor may be considered as forming a part of the second chamber 23.

Each of the walls 21 and 23 has substantially one way valve means 31thereon which permits the passage of air from the chamber 26 into thechambers 29 and 30 and hence into the chamber 28 when the air in thechamber 26 is compressed by movement of the diaphragm of loudspeaker 10toward the wall 22. On the other hand, when the diaphragm of the speaker10 moves toward the corner formed by the surfaces 11 and 12, the valvemeans closes prevent ing free movement of air from the chambers 29 and30 into the chamber 26. However, since the valve means 31 is notcompletely air tight when closed, there will not be a gradual reductionof air pressure in the chamber 26 during the period of operation of thespeaker 10. Instead, there will be only instantaneous or short-timevariations in the air pressure in the chamber 26, the time required forpressure equalization being several times greater than the period of thelowest frequency signal to be translated by the speaker 10.

The valve means 31 is shown in greater detail in Fig. 4. Although othertypes of valve construction may be employed, the construction shown inFig. 4 has been found to satisfactory results and comprises a move ableclosing member 32 which is hinged on the chamber wall, such as the wall21, by means of a flexible strip 33 which may, for example, be made ofleather. The strip 33 is secured to the wall 21 by means of screws ornails 34 and is secured to the member 32 by means of screws or nails 35.The member 32 strikes against a cushion strip 36 secured to the wall 21which strip 36 may, for example, be made of felt. The member 32 may bemade of wood. In one embodiment of the invention, the opening in thewall 21 is three inches square, the closing member 32 is four inchessquare and onehalf inch thick and the member 32, when closed, isapproximately one-sixteenth inch from the wall 21.

xcept for the valve means 31 and the openings be tween the chambers 28and 29 and the chambers 28 and 30, all of the chambers 26, 28, 29 and 30are substantially air-tight. The walls of the housing 14 should berelatively rigid and may, for example, be made of heavy plywood.

If the loudspeaker 10 has the ability to provide the desiredreproduction over the operating frequency range, then it is unnecessaryto mount additional loudspeakers in the housing 14. However, if it isdesired to employ additional speakers covering different portions of theoperating frequency range, such additional speakers 37, 38 and 39, maybe mounted in obturating relationship with apertures in the first wall15 and within the chamber 28. If a plurality of speakers are employed asshown, the speaker 10 may be employed to translate signals in the rangefrom 30-500 c.p.s., the speaker 38 may be employed to translate signalshaving a frequency in the range from 500-5,000 c.p.s., and the speakers37 and 39 may be employed to translate signals having frequencies in therange of 5,000 to 15,000, the signals being separated and supplied tothe various speakers in any conventional manner.

If it is desired to employ only two loudspeakers, the speakers 37 and 39and their corresponding apertures in the wall 15 may be omitted, theloudspeaker 10 being used to translate signals in the lower portion ofthe frequency range and the speaker 38 being used to translate signalsin the upper portion of the frequency range. Also, if desired to improvethe operation, the speaker 38 may be enclosed at the rear side thereofby a box 40 forming a chamber 41 at the rear of the diaphragm of thespeaker 38. On the other hand, the box 40 may be omitted andsatisfactory operation will still be obtained.

Most of the energy of audible sounds is contained in the fundamental orlow frequency waves. Accordingly, only the diaphragm of the loudspeakerwhich translates the lower frequency signals is required to performrelatively large excursions from a rest position and, therefore, itbecomes unnecessary as a practical matter, to attempt to equalize theair pressure on opposite sides of the diaphragm of the speakers such asthe speakers 3739 which translate the signals in the upper portion ofthe frequency range. It has been found that when provisions are made toequalize the pressure on opposite sides of the diaphragm of only thespeaker which translates signals in the lower portion of the frequencyrange, substantially distortionless sound production is obtained overthe entire audible frequency range. It is for this reason that the valvemeans 31 are provided only on the walls of the chamber 26.

It appears from a consideration of the operation in the apparatus shownin Figs. 1-3 that the excursions of the diaphragm of the speaker areundistorted by unequal air pressure even though the back waves aresuppressed because the valve means 31 prevents the build-up of pressureat the rear of the diaphragm of the speaker 10 during rearward movementof the diaphragm, but due to the closing of the valve means 31 duringthe forward movement of the diaphragm, a force is applied to thediaphragm which is proportional to the force applied to the diaphragmduring rearward movement thereof and caused by the resistance todisplacement by the air to such rearward movement. For this reason themovement of the diaphragm of the speaker 10 is equally retarded in bothdirections causing symmetrical movement of such diaphragm. If the valvemeans 31 were omitted, rearward movement of the diaphragm of the speaker10 would be retarded by the resistance of the air and forward movementof the diaphragm would be accelerated by expansion of the previouslycompressed air. The chambers 28-30 act as storage and absorbingchambers, and their combined volume preferably is at least equal to thevolume of the chamber 26.

Since the excursions of the diaphragm of speakers 37--39 are relativelysmall, it will be apparent that they will have little effect on theoperation of the speaker 10 and that they may be located in portions ofthe housing 14 other than those shown.

Although it will be understood that the housing 14 may have otherdimensions, the dimensions of one housing which I have constructed andhave found to give excellent results are as follows:

Length in inches 13 /2 29 /2 Dimensions:

The above dimensions are indicated on Figs. l-3.

If it is not possible to locate the housing of the loudspeaker apparatusadjacent a pair of mutually perpendicular surfaces, eg a corner of a.room, the embodiment shown in Fig. 5 may be employed. Fig. 5 is ahorizontal section View of an embodiment which may be located adjacent asingle surface 42 which may, for example, be a wall of a room. Theembodiment shown in Fig. 5 is constructed in accordance with theprinciples described above and comprises a housing 43 containing achamber 44 similar to the chamber 26 and a pair of chambers 45 and 46similar to the chambers 29 and 30. Valve means 31 are mounted on one ofthe walls of each of the chambers 45 and 46 and the loudspeaker 10 ismounted in obturating relationship with an aperture 47 on a wall 48 ofthe housing 43. The wall 48 tilts with respect to the surface 42 in thesame manner as the wall but usually the wall 48 is rectangular, asviewed from the surface 42, rather than tapered in order to obtain thedesired air volume between the wall 48 and the surface 42. The housing43 also contains a chamber (not shown) similar to the chamber 28 whichcommunicates with the chambers 45 and 46 and which may contain speakers37-69.

V In order to provide the desired air column in front of the diaphragmof the speaker 10, the side walls 49 and 50 of the housing 43 have apair of extensions 51 and 52 which are on opposite sides of the speaker10 and which extend toward the surface 42. The air column is locatedbetween the surface 42, wall 48 and the extensions 51 and 52. Withinpre-determined limits, the volume of the air column may be adjusted bymoving the housing 43 toward and away from the surface 42.

The embodiment shown in Fig. 5 does not provide sound dispersion andradiation as satisfactory as the embodiment shown in Figs. l-3. Inaddition, because of the size of the wall 48, difficulties, similar tothose described above in connection with infinite bafile systems, may beencountered. For these reasons, if it is not possible to locate theapparatus in a corner of a room, the embodiment shown in Figs. 6 and 7is preferable to the embodiment shown in Fig. 5. The embodiment shown inFigs. 6 and 7 comprises a housing 53 containing chambers 54, 55 and 56as well as an additional chamber (not shown) similar and oppositelydisposed with respect to the chamber 56. These chambers correspondrespectively to the chambers 26, 28, 29 and 30 shown in Figs. 'l-3. Thespeaker 10 is mounted on a wall 57 whose width is approximately equal tothe largest diameter of the diaphragm of the speaker 10 and thediaphragm of the speaker 10 faces into the corner formed by the surfaces58 and 59, which may be the wall and the floor, respectively, of a room.The speakers 37 and 38 are mounted on a wall 68 of the housing 53 andextend into the chamber 55. The chamber 56 as well as the oppositelydisposed corresponding chamber (not shown) are open at their upper endspermitting free passage of air between such chambers and the chamber 55.

The housing 53 is provided with a pair of extensions 61 and 62 whichseparate the housing 53 from the surfaces 58 and 59 providing airpassageways or columns between the wall 63 and the surface 59, betweenthe wall 60 and the surface 58 and between the wall 57 and the surfaces58 and 59. Such passageways or columns provide the desired air couplingto the speaker 10 as well as the desired sound dispersion.

While I have described the invention with reference to the preferredforms thereof, it will be understood by those skilled in the art, afterunderstanding the invention, that modifications and changes may be madetherein without departing from the spirit and scope of the invention asdefined by the claims appended hereto.

What is claimed as new and what I desire to secure by Letters Patent ofthe United States is:

l. A loudspeaker housing having a pair of chambers therein, an exteriorwall of one of said chambers having an opening therein adapted toreceive and be closed by a loudspeaker diaphragm, and one-way valvemeans interconnecting said chambers, said valve means permitting passageof air from said one chamber into the other of said chambers and atleast substantially restricting the passage of air from said otherchamber into said one chamber at the frequencies of operation of saidloudspeaker, and said other chamber being otherwise substantiallyair-tight. I

2. A loudspeaker housing having a pair of chambers therein, an exteriorwall of one of said chambers having an opening therein adapted toreceive and be closed by a loudspeaker diaphragm, and one-way valvemeans interconnecting said chambers, said valve means permitting passageof air from said one chamber into the other of said chambers and atleast substantially restricting the passage of air from said otherchamber into said one chamber at the frequencies of operation of saidloudspeaker, and said chambers being otherwise substantially air-tight.

3. Loudspeaker apparatus comprising a housing having a pair of chamberstherein, an exterior wall of one of said chambers having an openingtherein, a loudspeaker mounted in and closing said opening, and one-wayvalve 7 means interconnecting said chambers, said valve means permittingpassage of air from said one chamber into the other of said chambers andat least substantially restricting the passage of air from other chamberinto said one chamber at the frequencies of operation of saidloudspeaker, and said chambers being otherwise substantially air-tight.

4. Loudspeaker apparatus comprising a housing having a first air chambertherein, there being an aperture in said chamber, a loudspeaker drivingunit including a diaphragm mounted in obturating relation with saidaperture, one wall of said chamber having a one-way air valve thereinpermitting the escape of air from said chamber and at leastsubstantially restricting the flow of air into said chamber, saidchamber being otherwise substantially air-tight and said housing alsocomprising a second chamber in air communication with said valve forreceiving air from said first chamber, said second chamber beingotherwise substantially air-tight.

5. A loudspeaker housing comprising a plurality of joined walls forminga first chamber, one of said walls having an opening therein adapted toreceive and be closed by a loudspeaker diaphragm and one of said wallshaving a valve opening therein, a one-way valve mounted in said valveopening, said valve opening outwardly of said chamber and permittingsubstantially free outward flow of air from said chamber and preventingfree inward fiow of air into said chamber, and a further plurality ofwalls forming a second chamber exteriorly of said first chamber mountedto receive air from said first chamber through said valve opening, saidsecond chamber being otherwise substantially air-tight.

6. Loudspeaker apparatus comprising a housing having a first wall havingan aperture therein, a loudspeaker having a diaphragm, said diaphragmbeing mounted in and closing said aperture, said housing having aplurality of additional joining walls, a plurality of said additionalwalls forming a first chamber with said first wall which contains saiddiaphragm and the remainder of said additional walls forming a secondchamber adjacent said first chamber, one-way valve means interposedbetween said first chamber and said second chamber for permitting thepassage of air from said first chamber into said second chamber and atleast substantially restricting the passage of air from said otherchamber into said one chamber at the frequencies of operation of saidloudspeaker, said first and second chambers being substantiallyair-tight, and a pair of substantially imperforate extensions disposedon opposite sides of said aperture and extending outwardly from saidhousing the space between said extensions being substantiallyunobstructed in at least one direction substantially parallel to saidfirst wall.

7. Loudspeaker apparatus comprising a housing having a first wall havingan aperture therein, a loudspeaker having a diaphragm, said diaphragmbeing mounted in and closing said aperture, said housing having aplurality of additional joining walls, a plurality of said additionalwalls forming a first chamber with said first wall which contains saiddiaphragm and the remainder of said additional walls forming a secondchamber adjoining said first chamber, one-way valve means interposedbetween said first chamber and said second chamber for permitting thepassage of air from said first chamber into said second chamber and atleast substantially restricting the passage of air from said otherchamber into said one chamber at the frequencies of operation of saidloudspeaker, said first and second chambers being substantiallyair-tight, and a pair of said walls forming said first chamber with saidfirst wall and disposed on opposite sides of said aperture havingsubstantially imperforate portions extending outwardly from said housingand perpendicularly to the exterior surface of said first wall the spacebetween said extended portions being substantially unobstructed in atleast one direction substantially parallel to said first wall.

8. Loudspeaker apparatus adapted to be operated in a corner formed bytwo mutually perpendicular surfaces, said apparatus comprising a housinghaving a first wall adapted to face into said corner, a loudspeakerhaving a diaphragm, said wall having an aperture therein and saiddiaphragm being mounted in and closing said aperture and with the apexthereof extending inwardly of said housing, the distance between thesides of the portion of said wall having said aperture therein beingapproximately equal to the largest diameter of said diaphragm, saidhousing having a plurality of additional joining walls, a plurality ofsaid additional walls forming a first chamber with said first wall whichcontains said diaphragm and the remainder of said additional wallsforming a second chamber adjoining said first chamber, and one-way valvemeans interposed between said first chamber and said second chamber forpermitting the passage of air from said first chamber into said secondchamber and at least substantially restricting the passage of air fromsaid other chamber into said one chamber at the frequencies of operationof said loudspeaker, said first and second chambers being otherwisesubstantially air-tight.

9. Loudspeaker apparatus adapted to be operated in a corner formed bytwo mutually perpendicular surfaces, said apparatus comprising a housinghaving a first wall adapted to face into said corner, a loudspeakerhaving a diaphragm, said wall having an aperture therein and saiddiaphragm being mounted in and closing said aperture and with the apexthereof extending inwardly of said housing, the distance between thesides of the portion of said wall having said aperture therein beingapproximately equal to the largest diameter of said diaphragm, saidhousing having a plurality of additional joining walls, a plurality ofsaid additional walls forming a first chamber with said first wall whichcontains said diaphragm and the remainder of said additional wallsforming second, third and fourth chambers adjoining said first chamberand with said third and fourth chambers opening into said second chamberbut being otherwise substantially airtight, one-way valve meansinterposed in the opening between said first chamber and said thirdchamber and in the opening between said first chamber and said fourthchamber for permitting the passage of air from said first chamber intosaid third and fourth chambers, and said second chamber having anexterior wall having further aperture therein providing an opening intosaid second chamber but being otherwise substantially air-tight and aloudspeaker mounted in said further aperture and closing said furtheraperture.

10. Loudspeaker apparatus adapted to be operated in a corner formed bytwo mutually perpendicular surfaces, said apparatus comprising a housinghaving a first wall adapted to face into said corner, a low frequencyloudspeaker having a conical diaphragm, said wall having an aperturetherein spaced from the ends of said wall and said diaphragm beingmounted in and closing said aperture and with the apex thereof extendinginwardly of said housing, said aperture being spaced from said surfacesa distance which will provide an air column between said surfaces andthe center of said aperture which is substantially equal in volume totwice the volume of a cone having the shape and size of said diaphragmand the distance between the sides of the portion of said wall havingsaid aperture therein being approximately equal to the largest diameterof said diaphragm, said housing having a plurality of additional joiningwalls, a plurality of said additional walls forming a first chamber withsaid first wall which contains said diaphragm and the remainder of saidadditional walls forming second, third and fourth chambers adjoiningsaid first chamber and with said third and fourth chambers opening intosaid second chamber, said first chamber having a volume at least equalto the volume of said air column and the combined volumes of saidsecond, third and fourth chambers being at least equal to the volume ofsaid first chamber, one-way valve means interposed between said firstchamber and said third chamber and between said first chamber and saidfourth chamber for permitting the passage of air from said first chamberinto said third and fourth chambers, and said second chamber having anexterior wall having a further aperture therein providing an openinginto said second chamber and a high frequency loudspeaker mounted insaid further aperture and closing said further aperture.

11. Loudspeaker apparatus adapted to be operated in a corner formed bythree mutually perpendicular surfaces, said apparatus comprising ahousing having a base adapted to rest on one of said surfaces and afirst Wall adapted to face into the corner formed by the other two ofsaid surfaces and the outer surface of which slopes away from saidlast-mentioned corner from the base end thereof to the top end thereofat an angle in the range from 70 to 80 with respect to said base, aloudspeaker having a conical diaphragm, said wall having an aperturetherein spaced from said ends and said diaphragm being mounted in andclosing said aperture and with the apex thereof extending inwardly ofsaid housing, said aperture being spaced from said base end a distancewhich will provide an air column between said surfaces and belowsubstantially the center of said aperture which is substantially equalin volume to twice the volume of a cone having the shape and size ofsaid diaphragm and the distance between the sides of the portion of saidwall having said aperture therein being approximately equal to thelargest diameter of said diaphragm, said housing having a plurality ofadditional joining walls, a plurality of said additional walls forming afirst chamber with said first wall which contains said diaphragm andforming a second chamber with said first wall, said first chamber havinga volume substantially equal to the volume of said air column and thevolume of said second chamber being at least equal to the volume of saidfirst chamber, and oneway valve means interposed between said firstchamber and said second chamber for permitting the passage of air fromsaid first chamber into said second chamber.

12. Loudspeaker apparatus adapted to be operated in a corner formed bythree mutually perpendicular surfaces, said apparatus comprising ahousing having a base adapted to rest on one of said surfaces and afirst wall adapted to face into the corner formed by the other two ofsaid surfaces and the outer surface of which slopes away from saidlast-mentioned corner from the base end thereof to the top end thereofat an angle in the range from 70 to 80 with respect to said base, a lowfrequency loudspeaker having a conical diaphragm, said wall having anaperture therein spaced from said ends and said diaphragm being mountedin and closing said aperture and with the apex thereof extendinginwardly of said housing, said aperture being spaced from said base enda distance which will provide an air column between said surfaces andbelow substantially the center of said aperture which is substantiallyequal in volume to twice the volume of a cone having the shape and sizeof said diaphragm and the distance between the sides of the portion ofsaid wall having said aperture therein being approximately equal to thelargest diameter of said diaphragm, said housing having a plurality ofadditional joining Walls, a plurality of said additional walls forming afirst chamber with said first wall which contains said diaphragm andforming a second chamber with said first wall and the remainder of saidadditional walls forming third and fourth chambers adjoining said firstchamber and opening into said second chamber, said first chamber havinga volume substantially equal to the volume of said air column and thecombined volumes of said second, third and fourth chambers being atleast equal to the volume of said first chamber, one-Way valve meansinterposed between said first chamber and said third chamber and betweensaid first chamber and said fourth chamber for permitting the passage ofair from said first chamber into said third and fourth chambers, saidfirst wall having a plurality of further apertures therein providingopenings into said second chamber and plurality of high frequencyloudspeakers mounted one in each of said further apertures and closingsaid further apertures.

References Cited in the file of this patent UNITED STATES PATENTS1,891,968 Bidwell et a1 Dec. 27, 1932 2,337,213 Topping Dec. 21, 19432,491,982 Kincart Dec. 20, 1949 2,704,185 Travares Mar. 15, 19552,710,662 Camras June 14, 1955 2,757,751 Tavares Aug. 7, 1956 2,801,704Martin Aug. 6, 1957 2,834,423 Bradford May 13, 1958 FOREIGN PATENTS506,042 Great Britain May 19, 1939 OTHER REFERENCES Exponential Bafilesfor Custom Installations, by George Augspurger, Audio Engineering, vol.35-Issue, pages 24- 27, 67, published Nov. 1, 1951.

